Vehicles with electrically variable transmissions commonly operate in Electric Vehicle (EV) mode. In EV mode, the vehicle engine is shut down and the vehicle is driven by the transmission including the associated battery and motor/generators. Typically, a main transmission pump is used to operate the transmission during standard vehicle operation, i.e. when the engine is operating. However, the main transmission pump is typically powered by the vehicle engine. Thus, when the vehicle is in EV mode the main transmission pump is not powered and an auxiliary transmission pump is used to operate the transmission clutches, etc.
In cold climates the auxiliary pump fluid temperature can be low for a long period after the vehicle has been operating. The low fluid temperatures result from the location of the auxiliary pump and associated connections located outside of the transmission. Starting the auxiliary pump when the auxiliary pump fluid temperature is low may cause a pressure drop within the transmission fluid lines as the fluid from the auxiliary pump enters the transmission. The pressure drop effects the performance of the transmission clutches. Thus, the auxiliary pump may not be started until the pump fluid has reached a desirable operating temperature. Depending on the external temperature, this may take a significant amount of time. Since operating in EV mode is contingent on the use of the auxiliary pump, the vehicle is prevented from entering EV mode until the auxiliary pump fluid has reached the ideal minimum operating temperature.